Ultralight carbon aerogel with tubular structures and N-containing sandwich-like wall from kapok fibers for supercapacitor electrode materials

Abstract

Optimizing the structure of electrodes to decrease electrolyte transport resistance is essential for high electrochemical performance in supercapacitors. Here, we prepare ultralight carbon aerogels containing tubular structures and N-containing sandwich-like walls based on the natural structure of kapok fibers, by in-situ polymerization of pyrrole and carbonization. The resulting carbon aerogels are composed of microtubes with a diameter of 10 μm, an ultralow density of 6 mg cm−3, and also N-containing sandwich-like walls composed of pyridinic nitrogen, pyrrolic/pyridine nitrogen, and quaternary nitrogen/oxidized nitrogen. The unique tubular structure promotes transport of electrolyte, yielding higher electrochemical performance. Consequently, the tubular structure produces a 72 F g−1 increase in the capacitance compared with that of a cattail carbon aerogel without a tubular structure. The N-containing sandwich-like walls provide more active sites, greater pseudocapacitance, and increase the thickness of the microtube to protect the tubular structures from damage during carbonization. Specifically, the optimal sample has a specific capacitance of 274 F g−1 at a current density of 1 A g−1 with an energy density of 8.51 Wh kg−1, a superior rate capability, and excellent cycling stability with a capacitance retention of 97.7% after 4000 cycles.